Manufacture of diazo type material



Patented May 9, 1939 PATENT oer-Ice HANUIAG'I'UBS 0F D1570 TYPE MATERIAL Walker-H. Hinman.

IlL, minor-to Winnetka, 'llreFrederlokloctOomnany,0hicago,lll.,a

c rporation of Illinois No mm. Appllcaflon January 0, 19:1, BerialNo. 11am 2 Claims.

The present invention relates to diazotypes and has particular relation to the appearance of the print with respect to changes in the background.

Diazotypes are positive prints made upon sensitized paper by the printing action ot'actinic light through a light transmitting pattern. A sensitizing substance is used which is capable of union witha coupling agent to create a (westud. The sensitizing substance can be destroyed -by light, so that where light strikes, no dye can form. The light-printed sensitized papers vary in composition and may be developed in various ways, as by water, or by developer solution, or by ammonia vapors, and then dried. The fresh dry print should have no color where it is struck by light, and hence on white paper should show a white ileldor backgroundior a lined drawing. Under the influence of ordinary light acting for a. long time, or of strong light acting for a shorter time, .a so-called discoloration appears as a yellowing or browning oi the originally whiter field. I

Various attempts have been made to avoid this coloration or so-called' discoloration. One of these has been to use a reducing agent in the print. This is only partially effective, and quite suitable for ordinary uses, but not for strong sunlight. other attempts have been made to the color change by employing a paper e from dyed stock. In one instance a. green paper was used, but when the coloration occurred the colored face and the green back were quiiecontrusting. But a white and not a colored background is commercially desired.

The present invention aims to avoid the eflects oi discoloration by masking the same, and to provide a white prlntlacking in severe contrast between its face and its back, when freshly made and when aged to the extent that it would appean dlscoloredif on a pure white stock.

The present invention takes advantage of .the power of a light blue color to mast: a yellow or tan on white, and to give the appearance of white.

The unqualified word "white is not used in its true technical sense, which means a neutralizing mixture of all visible color, but rather in its commercial sensewith reference to the color 01" socalled white" papers. A white paper may be on the yellow, or the blue, or some othercolor, and yet be called a white paper. The character of whiteness" is more apparent when comparing, side-by-side, two differently white papers. For. example, the face of a slightly discolored diaaotype on a white stock may look white by itself, but when it is compared to the back 0! the print, it will appear pale yellow or tan. The exact color may depend a great deal upon the residual chemicals left in the print, and these may vary with the character of the sensitizing solution, or the (GI. 9H)

character of the developer, or with the treatment oi the print.

It has been observed that a blue-white is not so contrasting with a better white, as is a yellowwhite. Therefore, the invention contemplates using a stock which is white on one side and a bluer white-on the sensitized side. when a print is dry and not discolored from the effect of light, the white back of the print is not highly contrasting with the bluer white face. Then as yellow or tan is produced on. aging, the newly termed color is "neutralized by the blue which is present.

The above statement is perhaps merely a, practical statement or the invention, which pets;

the results to be understood. But it may not explain the mechanism. It is suggested that the action or the blue may not be entirely or par-- tially one oi neutralization, but rather one or filtering out or absorbing certain light rays or fractions thereol which sheet the discoloration.

As mentioned above a reducing agent y be used to as discoloration as set forth in the ,Van der Clrinten U. S. Patent No. 1,821,281 and No. 1,841,653. In that patent it is set forth that the reducing agent may be added in one or numerous ways or in a combination oi is may be present in the paper before coatint.v in the coating solution, in the developer, or be spe clally applied after the print is completed. The present invention may be used with or without a reducing agent which may be applied according to said patent. The combination use oi blue and oi reducing agent is more effective than use of the blue alone, or use oi the reducing, agent alone. The reducing agent retards the formation of discolori'ng material, and the blue color masks it when and it it doesiorm. hpaper having reducing agent which may get yellow in strong sunlight, will appear less yellow it the blue is present. a

' The invention may be carried out in numerous ways. The blue color may be impr or applied to one side oi the stock sheet to be sensitized, or laminated sheet stock may be used with a white racing sheet and a bluer white facing sheet. The objective is to have the back side white, with the face 'abluer white. The blue color may be applied in a sizing bath with which the stock may be sized on its face. Also the blue color may be applied in the sensitizing solution. Developer solution or wash water may be used with blue color therein to apply the blue tint, and it may even be applied after the print is completed. Several of these ways may be used in combination.

A preferred method of applying the blue color has been found. That is to apply it from the sensitizing solution. For the purpose or the til to the sensitizing solution to give a blue tint to the background of the finished print, for example enough Pontacyl Brilliant Blue 2R, made by E. I. du Pont de Nemours of Wilmington, Delaware, to make the bath about .04% in such dyestuif. This is coated directly onto theface of white paper stock and dried. The diazo solution may be colorless or colored, depending in one respect upon the color of the diazo compound employed. Where a yellow diazo solution is used, the dried sensitized sheet looks white on the back and green on the coated face. Upon light-printing the face of the sheet becomes blue-tinted where struck by light, and remains green only where the image of the pattern lies. This green image may be strengthened by a developer.

The invention may be carried out as follows:

An ordinary sensitizing bath may be used, such as one containing Grams per liter Chlorostannate of para. dlazo di-n-butyl aniline 20.0 Pontacyl Brilliant Blue 2R. .4

Water.

. Grams per liter Sodium carbonate (monolnrdrate) 10 Phloroglucinol 4 The paper is merely wet with the developer, and it need not but may be washed afterwards. If the print is to be made more resistant to discoloration in strong light, reducing agent may be added as above mentioned. This may be conveniently done by adding 30 grams per liter of sodium thiosulphate to the above developer solution when the developed print is not to be washed. The dry print is then without strong contrast between its face and its back, and this close identify of the back of the print and the background of the face continues and remains under conditions where the same print lacking the blue color would show a contrast between a white back and a discolored face. I

It is preferred to apply the color in the sensitizing solution for several reasons.- The color itself appears to be more .permanent against fading in light, when it is applied from the sensitizing bath, than when it is applied directly to the paper beforesensitizing. By this method the dye appears to be more a part of the chemicals than a part of the fiber. Hence it can be effective on chemicals lying between fibers or on fibers. Also it has been found that the blue color applied from the sensitizing bath renders the unprinted sensitized sheet-more stable for storage'before use. Ithas better keeping qualthe results, the same can be readily explained. The invention may depend upon the defects of human vision in correctly analyzing color values. The whites cover a wide range. of tints. Since a truly white object reflects white light waves without change in proportion to give the color white, the added reflection of slightly more light of one color to give a tint, is not very noticeable. For example, the blue of the tint is merely an addition to the blue component of white light. In other words the amount of white which is present more or less blinds the eye to the tints. This is more true of blue than of yellow, because the eye is more sensitive to yellow. It is known that to the eye a mixture of blue and yellow makes green. Since green is considered a restful color to the 7 eye, the eye is not quick to note it, as-it does yellow. It is therefore believed that the blue changes the reactions of the eye, by eliminating the response it would get from yellow and substituting the less response it gets from green.

The foregoing physical theory is substantiated by the fact that any blue colors may be used, and by the old well known result of using blueing in washing.

The invention may be used with diabotypes in general. There are two possible primary sources of yellowing in the background. One is the residue of the sensitizing substance after it is decomposed by light. The other is residual coupling agents which may be in the paper or in the developer. It is known for a certainty that it may be one or both together which are culpable. It is recognized that the residual sensitizing solution may contain a phenolic substance.

The coupling agents are commonly phenolic substances, and phenolic substances are discolored by light.

As set forth in the Van der Grinten patent the yellowing with age in light is a general characteristic of diazotypes, irrespective of the characters of the diazonium compound and of 'the coupling agents used'. Upon these also depends the color of the pattern printed. The present invention is useful in place of the addition of the reducing agent of Van der Grinten, or as an addition to it.

The invention is of course not limted to the example given and such changes and modifications are intended as fall within the scope of the invention defined in the appended claims.

I claim:

1. A diazotype print having a commercially white back and face, the face having an additional blue tint not present in the back, the two whites being of such character that there is absence of sharp contrast between the face and the back, the said blue tint in the face serving to avoid a contrast between the face and the back upon aging of the print with the background of the face exposed to light.

2. A light-sensitive sheet comprisng a white sheet-coated on one side with alight-sensitive dia'zo composition with which is associated a blue coloring agent to -give the coated side a blue component in its color, said blue color serving later in a diazotype made from said sheet to maintain a non-contrasting white appearance of the two faces under exposure to light sufficient to discolor to the eye the background of the print in the absence-of such blue. color.

WALKER M. HINMAN. 

